Blood is a complex mixture composed of plasma and cells [(Beck W S (Ed.). Hematology. MIT Press 1985; Bloom A L, Thomas, D P (Eds.). Haemostasis and thrombosis. Longman 1987; Janeway C A, et al., Immunobiology. Elsevier 1999)]. The plasma can be separated from the cells by centrifugation and other techniques. If the plasma is allowed to stand it will clot by coagulation and serum may be separated from the blood clot. The coagulation may be inhibited by addition of various anticoagulants, including EDTA, EGTA, heparin, citrate and others. The cells of the blood include dendritic cells, macrophages, monocytes, neutrophils, T lymphocytes, B lymphocytes, natural killer cells, red blood cells and various stem cells including hemopoietic stem cells. In addition megakaryocyte-derived platelets are present in large numbers. The plasma contains thousands of proteins, in principle any protein of the human proteome [Thadikkaran L, et al, Recent advances in blood-related proteomics. Proteomics. 2005; 5:3019-34; Anderson N L and Anderson N G. The human plasma proteome: history, character, and diagnostic prospects. Mol Cell Proteomics. 2002; 1:845-67)]. Some of the proteins are involved in transport, blood clotting or immune defence, while others function as signalling molecules between cells of the blood and cells of the tissues. In particular, the activity of the cells of the immune system (dendritic cells, macrophages, T cells, B cells, natural killer cells) is regulated by a complex network of signalling molecules (e.g. interleukins, chemokines, growth factors), tissue antigens and receptors (Janeway, cited above; Steinke J W, et al, Cytokines and chemokines. J Allergy Clin Immunol. 2006; 117:S441-5; Blach-Olszewska Z. Innate immunity: cells, receptors, and signaling pathways. Arch Immunol Ther Exp. 2005; 53:245-53. Lapidot T, Petit I.
Current understanding of stem cell mobilization: the roles of chemokines, proteolytic enzymes, adhesion molecules, cytokines, and stromal cells. Exp Hematol. 2002; 30:973-81. Cravens P D, Lipsky P E. Dendritic cells, chemokine receptors and autoimmune inflammatory diseases. Immunol Cell Biol. 2002; 80:497-505.] The activity and specificity of immune system cells can be investigated and quantitated by several methods and assays. T cells, B cells and other cells can be quantitated by fluorescence-activated cell sorting using antibodies to cell surface marker molecules (Villas B H. Flow cytometry: an overview. Cell Vis. 1998; 5:56-61. Stelzer G T, Robinson J P. Flow cytometric evaluation of leukocyte function. Diagn Clin Immunol. 1988; 5:223-31.] Specific T cells can be measured by cytotoxicity assays, chromium release assays and cytokine release assays (e.g. ELISPOT) (Jerome K R, et al., Measurement of CTL-induced cytotoxicity: the caspase 3 assay. Apoptosis. 2003; 8:563-7; Andersen M H, et al, Cytotoxic T cells. J Invest Dermatol. 2006; 126:32-41. Troutt A B, et al, Quantitative analysis of lymphokine expression in vivo and in vitro. Immunol Cell Biol. 1992; 70:51-7; Schmittel A, et al., Quantification of tumor-specific T lymphocytes with the ELISPOT assay. J Immunother. 2000; 23:289-95; House R V. Theory and practice of cytokine assessment in immunotoxicology. Methods. 1999; 19:17-27.) and by using various peptide-major histocompatibility complex (MHC) protein constructs (Meidenbauer N, et al, Direct visualization of antigen-specific T cells using peptide-MHC-class I tetrameric complexes. Methods. 2003; 31:160-71; Bousso P. Generation of MHC-peptide tetramers: a new opportunity for dissecting T-cell immune responses. Microbes Infect. 2000; 2:425-9). The activity of B cells can be measured by determining the levels of specific antibodies released from the B cells (Hogrefe W R. Biomarkers and assessment of vaccine responses. Biomarkers. 2005; 10:S50-7; Manz R A, et al, Maintenance of serum antibody levels. Annu Rev Immunol. 2005; 23:367-86).
A major problem in measuring signalling molecules released from blood cells is that of storage and transport in relation to quantitation. Many blood constituents (e.g. cytokines) are labile and short lived, resulting in degradation during incubation, storage and transport. For this reason, comparative analyses and diagnostic tests have to be carried out immediately upon blood collection and incubation in central laboratories. Ideally, all samples to be compared should be analyzed consecutively using a calibrated instrument.
This is not always practical, e.g. when taking blood samples in remote areas, when doing in vitro and in vivo time-studies or when comparing samples from many different individuals. One solution to this problem is to freeze samples for transport and storage. This, however, does not guarantee preservation of constituents, requires large freezing, transport and storage capacity, requires thawing each time an analysis is performed, and is vulnerable with regard to shortage of electric power supply. For this reason, there is a need for reliable methods of blood and biological sample preservation and a need for diagnostic tests employing reliable sample preservation in combination with sample manipulation.
The use of filter paper for spotting blood for subsequent analysis is well known, e.g. for analysis of blood samples of newborn babies for inherited metabolic diseases (Mei J V, et al., Use of filter paper for the collection and analysis of human whole blood specimens. J Nutr. 2001; 131:1631S-6S. The advantages of this are good preservation of blood constituents, easy transport and facile long term storage. However, the use of filter paper and similar methods for drying and storing blood samples after incubation with test compounds has not been used or described before, possibly because this has been anticipated to be impossible or impractical.
What are needed are improved methods for transporting and storing biological samples.